1. Field of Invention
The present invention relates generally to actuator systems for generating pressure fluctuations and, more particularly, to circumferential actuator systems for actively controlling and generating pressure fluctuations in piping systems.
2. Brief Description of Related Art
Generation of precise pressure fluctuations in piping systems is desirable for a number of reasons. The ability to generate known and arbitrary pressure fluctuations is advantageous for diagnostic purposes, e.g., for determining how a piping system will respond acoustically once assembled. Also, by providing a known pressure pulse to a piping system and then measuring the pressure at a point downstream, one can determine whether the system has leaks. To actively control the fluid-borne energy, and thus the acoustic radiation, of a piping system it is necessary to produce precise pressure fluctuations. For example, to reduce downstream pressure fluctuations, it is necessary to control signal generation such that a pressure wave equal in magnitude but 180.degree. out of phase with the incoming pressure wave is generated. Furthermore, by generating waves in a fluid filled tube, the acoustic impedance of a material immersed in the fluid may be determined.
However, presently there are no actuator systems designed specifically for use on pipes. Known actuators, such as for example J-9 actuators manufactured by Argotec, are designed to be submerged in water to operate as a sound source. Adapting known actuators for use with piping systems has produced unsatisfactory results.
Most prior art actuators are bulky with large, flat vibrating surfaces. Consequently, a number of problems arise. Present actuator systems are design to act against the total pressure (static pressure+dynamic pressure) of the fluid in which they are submerged. To produce a satisfactory pressure wave, the actuator requires a large internally mounted inertial mass and high power to move the mass to produce vibrations at the vibrating surface. As a result, when mounted on a pipe, heavy prior art actuators (e.g., the J-9 actuator weighs over 30 lbs) create non-symmetrical structural changes to the piping system. Moreover, because the large vibrating face is flat, the actuator acts as a point source. Thus, a discontinuity in the pipe is created. Depending on the diameter of the pipe, the vibrating face of the actuator covers a different percentage of the circumference. Therefore, it is difficult, if not impossible, to supply uniform pressure fluctuations among various sized piping systems.
It is impossible to vary the amplitude and phase of generated higher order mode pressure fluctuation with a single actuator. If the diameter of the pipe is large enough, more than one prior art actuator may be mounted around the circumference and the amplitude and phase of each actuator may be controlled independently. However, there is no existing apparatus for accurately controlling the actuators as a unit to produce a desired pressure fluctuation mode. Additionally, due to size constraints, it is difficult, if not impossible, to cover a sufficient amount of the circumferential surface to allow adequate control of the generated pressure fluctuations. Furthermore, a single actuator or single axially aligned set of actuators spaced around the pipe circumference will produce a pressure wave that propagates both upstream and down stream. By traveling upstream, the pressure wave interacts and interferes with the boundary conditions of the piping system.
Presently there is no system for accurately and actively generating pressure fluctuations in piping systems. Consequently there is a need for an actuator system for actively controlling and generating pressure fluctuations.